The ultimate guide to Ruby concurrency interviews. Developed by FAANG engineers, this course covers Monitors, Deferred Callbacks and problem-solving strategies for Reader-Writer and Dining Philosopher Problems.

Concurrency in Ruby is one of the most complex and advanced topics brought up during senior engineering interviews. Knowledge of concurrency and multithreading can put interviewees at a considerable advantage. This course lays the foundations of advanced concurrency and multithreading and explains concepts such as Monitors and Deferred Callbacks in depth. It also builds simple and complete solutions to popular concurrency problems that can be asked about in interviews like the Reader-Writer Problem and the Dining Philosopher Problem. While prior knowledge of concurrency is not required to follow through with this course, familiarity with the basics of Ruby would be helpful.

Ruby Concurrency for Senior Engineering Interviews

<div class="ans">
# Monitor Mixin

<p>A mixin, when added to a class, augments it with additional capabilities without using inheritance. In Ruby, a mixin is a code wrapped up in a module that a class can include or extend. The standard library offers a mixin called <code class="clazz">MonitorMixin</code>. We can either include it in our class or extend an object of our class with it to gain monitor functionality.</p>

<p>Let's consider an example class <code class="clazz">Person</code> as follows:</p>

```ruby
class Person
  def initialize()
    @count = 0
    @name = "unnamed"
  end

  def updateName(name)
    @name = name
    @count += 1
  end

  def to_s
    return "I am #{@name} updated #{@count} times."
  end

end
```
<p>The class is trivial and has only two instance fields. One is the name of the person and another is the count, which keeps track of how many times the name gets updated. The method <code class="mthd">updateName()</code> isn't thread-safe. Multiple threads writing to it can step over each other's changes. One way we can fix this is to include the <code class="clazz">MonitorMixin</code> in the class and then use <code class="clazz">synchronize</code> or <code class="mthd">mon_enter()</code> and <code class="mthd">mon_exit()</code> methods to protect the critical sections. This implementation appears in the code widget below:</p>


</div>


<div>
# Monitor Mixin

<p>A mixin, when added to a class, augments it with additional capabilities without using inheritance. In Ruby, a mixin is a code wrapped up in a module that a class can include or extend. The standard library offers a mixin called <code>MonitorMixin</code>. We can either include it in our class or extend an object of our class with it to gain monitor functionality.</p>

<p>Let's consider an example class <code>Person</code> as follows:</p>

```ruby
class Person
  def initialize()
    @count = 0
    @name = "unnamed"
  end

  def updateName(name)
    @name = name
    @count += 1
  end

  def to_s
    return "I am #{@name} updated #{@count} times."
  end

end
```
<p>The class is trivial and has only two instance fields. One is the name of the person and another is the count, which keeps track of how many times the name gets updated. The method <code>updateName()</code> isn't thread-safe. Multiple threads writing to it can step over each other's changes. One way we can fix this is to include the <code>MonitorMixin</code> in the class and then use <code>synchronize</code> or <code>mon_enter()</code> and <code>mon_exit()</code> methods to protect the critical sections. This implementation appears in the code widget below:</p>


</div>


This lesson continues the discussion on Monitor in Ruby.

The Basics

API Overview

Brief Intro to Asynchronous Programming

Interview Practice Problems

Bonus Questions

Epilogue

... continued

Monitor Mixin